Tunisia’s interior minister says that four suspects belonging to a radical Islamist group are being held over their involvement in the murder of a leftist opposition politician earlier this month that plunged the country into a political crisis.

Ali Larayedh said Tuesday that the suspects, some of whom had been arrested in the past 48 hours, were just accomplices to the murder and did not include the assassin himself.

Chokri Belaid was shot four times outside his home on the morning of Feb. 6, provoking widespread rioting around the country as many held the government responsible for his death.

Thousands demonstrated oSunday, protesting the lack of progress in solving the crime, which was seen as a symptom of the rising violence in Tunisia’s politics.